1. Field of the Invention
The present invention relates to an insulation housing and card guide, and more particularly to an insulation housing and card guide for mounting on a substrate. The present invention also relates generally to the combination of a printed circuit board having mounted thereon a plurality of electrically conducting post-type contacts, enclosed by a removable electrically insulating housing latchably secured to a selected contact, and also to a multi-layer printed circuit board and a method of fabrication thereof. The present invention further relates to a method and apparatus for assembling electrically conductive posts to a substrate, and more particularly to method and apparatus for assembling conductive post-type contacts to a substrate which advantageously permits positive location and anchoring of a connector housing to the substrate and in enclosing relationship over the assembled contacts.
2. Description of the Prior Art
The present invention satisfies the need for a low electrical insulation housing for containing a plurality of electrical terminals mounted to a substrate such as a printed circuit board. The invention further satisfies the need for inexpensive guides for a card which is to be electrically connected to and disconnected from the plurality of electrical terminals contained within the insulation housing. In addition to the objective of low cost, the card guides associated with the housing should be free of warpage and misalignment in order to receive and permit removal of a card without binding. In meeting these objectives, the insulation housing according to the present invention is not directly connected to the printed circuit board or substrate. Instead, the housing is advantageously detachably latched to the electrical terminals mounted on the substrate. The housing thereby serves as a shroud for protecting the electrical terminals and may be readily removed when desired. Each housing includes a pair of channel guides for receiving therebetween opposed margins of a card. Each channel is connected to the housing by an integral hinge or neck portion. This feature permits the rails to flex resiliently in cantilever fashion to enhance alignment thereof so that a card may be received between the channels without binding. The card guide channels of a plurality of housings are connected to a common stiffener rail to prevent warpage and twisting of the channels.
The electrical terminals to which the insulation housing is detachably latched comprises a first conductive post portion offset from a second conductive post portion, with a shelf portion for receiving the edge of the card in registration thereagainst. Adjacent to the shelf portion, each terminal is provided with a lateral notch portion. When a plurality of the posts are mounted to the substrate, the notch portions of selected ones of the terminals are arranged in aligned generally coplanar relationship. The insulation housing is received over a plurality of the terminals and includes an inner linear projection or flange portion which latchingly registers within the aligned notch portions of the terminals. Accordingly, the housing is fixedly mounted to the substrate without a need for a direct mechanical connection therebetween. The housing is advantageously detachable from the substrate by resiliently flexing the sidewalls and disengaging the flange portion thereof from the notch portions of the terminals.
As a further feature, the shelf portion of each terminal is provided with a frangible stem for connection to a carrier strip. Thus the carrier strip allows the terminals to be advantageously supplied and handled. The terminals are readily disconnected from the substrate by individually detaching each terminal from its frangible stem.
The present invention is also directed to fabrication of an electrical panel including a board substrate into which a plurality of electrically conducting post-type contacts are inserted. Post portions of the contacts protrude from one side of the substrate and advantageously receive point-to-point electrical wiring. Other portions of the posts protrude from the opposite side of the substrate to form electrical contacts suitable for electrical registration with electrical paths of a printed circuit board or card. In most applications, an electrically insulating connector housing insulates and protects the contact portions of the posts. The housing also must be secured on the surface of the substrate. In many cases the substrate is provided with plated circuit paths in addition to the point-to-point wiring provided by the conducting posts.
Heretofore time consuming successive steps were required to fabricate such a panel. Initially the contacts were inserted individually within the connector housing. The contacts has to be individually latched in the housing to prevent removal therefrom. As a practical matter, the housing provided a plurality of individual sockets having internal latching structure for receiving and latching onto an individual contact. The internal structure of such a connector housing was necessarily complex and was costly to design and fabricate. A great deal of time was expended to insure insertion and latching of each individual contact within a socket of the connector housing. Additional time was expended to assemble the connector housing and the retained posts to the substrate. Fasteners such as screws and the like were required to attach the connector housing to the substrate surface. The posts then protruded through the apertures in the substrate to receive the point-to-point wiring.
If it was desired to electrically connect the post-type contact to plated electrical paths of the substrate, each post portion was separately hand soldered to a plated path. This procedure resulted in satisfactory electrical joining, but was time consuming.
Some attempt was made to reduce the assembly time by sliding solder rings over the posts to be soldered, and simultaneously reflowing the solder by the application of heat, in an attempt to simultaneously solder all the posts to the plated paths. Often times the reflowed solder was of insufficient mass, or did not sufficiently wick into the substrate apertures to create a strong solder joint. This required inspection and testing after soldering to insure electrical continuity of the solder joints. Those joints which did not produce electrical continuity had to be repaired by hand soldering. Also those joints which produced electrical continuity but were structurally weak and subject to breakage at a later time also had to be replaced by hand soldering. It is not uncommon in a panel as above described to have a thousand soldered posts. If only one post in a thousand has an insufficient solder joint, representing a failure rate of 0.1%, then statistically every single panel would be inoperative if fabricated according to the above described assembly procedures. Thus there has been a long existing need in the prior art for a method of reliably assemblying a plurality of electrical contacts mechanically and electrically to a substrate and suitable for use with a connector housing enclosing the contacts.
In the present invention, a plurality of electrically conducting posts individually depend from a carrier strip on precise center spacings. The posts can be simultaneously assembled into apertures of a substrate having corresponding center spacings. Each post is provided with an encircling band of solder which registers internally of a corresponding substrate aperture. Advantageously upon reflow of the solder bands, each post is reliably mechanically and electrically joined to the substrate. This assembly procedure reduces the assembly time required for insertion of individual contacts. Assembly time is further reduced by simultaneously reflowing the solder bands of all the conducting contacts desirably inserted into the substrate. This eliminates the need for individually treating each post, either by hand soldering, or by applying solder rings individually over each contact subsequent to assembly of the posts in the substrate.
Each of the contacts is attached at its terminal end to the carrier strip with no interconnection between adjacent posts. This permits individual guiding of the posts into respective substrate apertures without undue bending or deflection of the carrier strip or the individual posts. The carrier strip supports the contacts in mutual alignment and on desired center spacings in the board.
By providing the solder bands on the posts prior to insertion in the substrate, the solder bands will be located radially internally of the apertures. Each solder band is of a selected band width to provide sufficient solder mass for filling the space between the lined aperture and the post inserted therein, and for the formation of fillets encircling and adhered to a conducting post at each end of a lined aperture. In addition, the solder band is precisely located internally of the lined aperture, such that upon reflow solder will ahere along the entire length of the aperture lining. Such a joint is more reliable than a hand soldered joint or the application of solder rings to the posts after insertion.
Soldering to the posts after insertion requires wicking of molten solder into the lined substrate apertures. A joint produced by this wicking action has a relatively high probability of failure. One cause of failure results from insufficient solder mass to completely fill the space between the lined aperture and a post inserted therein, even though solder fillets are formed at each end of the aperture. The presence of the solder fillets prevents inspection for solder voids internally of each aperture. Another cause of failure results from insufficient wicking action of solder internally of an aperture. Either of these results can produce failure, which is immediately detected by testing for electrical continuity. Even if electrical continuity is initially established the joint itself is structurally weak and will later fail upon breaking of the joint when subjected to normal handling and use.
The present invention is well suited for reducing panel assembly time, since the conducting posts are utilized to locate and anchor an enclosing connector housing to a substrate without the need for additional fasteners. According to one preferred embodiment, a connector housing is provided over the inserted contacts and is latchably joined thereto. As an alternative, the contacts may be inserted into the substrate and the connector housing simultaneously. In this embodiment, reflowing of the solder bands provided on the posts is accomplished with the connector housing in place on the substrate.
As a further feature of the invention, since the posts remain attached to their carrier strip until positively joined to the substrate by reflowing of their solder bands, they remain in desired alignment without the need for individual aligning slots in the connector housing. Accordingly, the present invention allows for the use of a connector housing with relatively simple interior structure. This further reduces panel assembly time since the posts need not be interfitted within individual slots during assembly. In addition, the costs of material and fabrication in the connector housing itself are substantially reduced due to its relatively simple interior structure.
In addition, each of the contacts according to the present invention is provided with a selected mass of solder adhered thereto in a selected band width and positively located on a selected medial portion of the contact. Each contact is further provided with structure for locating it in position on a printed circuit board, for limiting insertion thereof in a printed circuit board, as well as for positively positioning the solder band interiorly of a plating lined hole of the board into which the contact is inserted.
Each contact is additionally provided with structure to which a portion of the encircling insulation housing is removably latched.
The insulation housing includes an integral latch portion. When the housing is received over a plurality of contacts according to the present invention, the latch portion will resiliently register in latching relationship on a selected one of the contacts, advantageously securing the housing to the selected contact and thereby in fixed mounted position on the printed circuit board. To remove the housing, a tool may be used to manually pry the resilient latch portion to disengage it from the selected contact and allow removal of the housing from the enclosed plurality of contacts.
According to a feature of the present invention, when all the desired number of contacts are mounted in corresponding plating lined apertures of the printed circuit board, all the solder bands of the posts are simultaneously heated to reduce the solder bands to a molten state and reflowed by wicking action into the clearances defined between the contacts and the apertures receiving the contact to make positive electrical and mechanical connections of the contacts to the plating lined apertures. Such connection technique is disclosed in copending application Ser. No. 193,366, filed Oct. 28, 1971.
Another salient feature of the present invention is practiced during connection of the contacts to the printed circuit board. More specifically, the plating lined apertures of the boards are arranged in rows, each row receiving a corresponding row of contacts inserted therein. A common carrier strip remains attached to the individual ends of corresponding contacts in each row. The carrier strip retains the contact ends in desired alignment during reflow of the solder, in accordance with the disclosure of copending application Ser. No. 193,366, filed Oct. 28, 1971. The medial portions of the posts in each row are maintained in desired alignment since they are received in the corresponding plating lined apertures of the board. The free ends of the contacts of each row, namely the ends which are not connected to the carrier strip, are received in apertures of an auxiliary board or substrate. The apertures of the auxiliary board are on the same center spacings as are the plating lined apertures of the printed circuit board. Thus such free ends of the contacts of each row are maintained in desired alignment by the auxiliary board. The contacts are maintained in alignment by the carrier strip, the printed circuit board and the auxiliary board while the solder bands are heated are reflowed, then subsequently allowed to cool in order to form rigid solder joints positively connecting individual contacts mechanically and electrically to the plating lined holes of the printed circuit board. Upon cooling of the reflowed solder, rigid joints are obtained, allowing removal of the auxiliary boards and the common carrier strip portion from each row of posts without disturbing the desired alignment of the contacts in the printed circuit board.
According to a further feature of the present invention, the contacts provided with solder bands may be utilized to connect together a plurality of printed circuit boards in stacked relationship. Generally, a single printed circuit board has a limited surface area which accordingly limits the number of plated circuit paths which can be adhered to the surface. It is common to use both a top surface and a bottom surface of a printed circuit board for carrying printed circuit paths. It is often desirable to use a second printed circuit board additional circuit paths which would not otherwise fit on a single printed circuit board already crowded with circuit paths. It is also often desirable to provide design changes on a secong printed circuit board. Use of a second board obviates the need to discard the original printed circuit board in favor of a redesigned board. Thus, there are many instances where two printed circuit boards are favored over the use of a single board. Where two boards are desirable, it is necessary to electrically interconnect the circuit paths of the two boards. According to the present invention, a plurality of boards may be utilized in stacked relationship, with the required electrical interconnections between such boards being accomplished by a plurality of contacts according to the present invention received in plating lined apertures of the boards. To provide a positive electrical interconnection between the boards, the solder bands of the interconnecting contacts are reflowed and then cooled to form solder joints, thereby electrically and mechanically connecting the contacts to plating lined apertures of the stacked boards. To substantially reduce assembly time, it is advantageous that all the contacts be inserted in the plating lined apertures of the stacked boards, and all the solder bands of the inserted contacts be simultaneously reflowed and then cooled to form the individual solder joints. During solder reflow and cooling to form the joints, alignment of the contacts is assured by utilizing the attached carrier strip and auxiliary board alignment technique as above described.
The present invention is particularly useful for fabricating a multi-layer printed circuit board. Generally, a multi-layer board includes a plurality of stacked planes with circuit paths being carried in a plurality of such planes. Interconnections are required between circuit paths of different planes. The location of such interconnections between planes as well as routing of the plated paths themselves are of such design complexity that automated computer design is required. In addition, fabrication of the multi-layer board must also be accomplished by automated techniques. The present invention permits design and fabrication of a multi-layer board without the need for expensive automated computer equipment. It therefore provides a technology enabling the design and fabrication of complex electronic circuit boards without a need for investing in expensive automated equipment. The present invention accordingly enhances entry of small companies into the industry of complex electronic circuitry dominated by a relatively few large companies.